Adjustable Implant

ABSTRACT

An adjustable implant includes a telescopic body with first and second portions in sliding engagement, and a deflectable linkage formed from a first linking segment, an intermediate segment and a second linking segment pivotally interconnected so that adjustment of a length of the telescopic body causes a corresponding deflection of the deflectable linkage. The first linking segment and the second linking segment are formed with projecting features that provide a partial gear engagement between the first and second linking segments such that, during adjustment of a length of the telescopic body and corresponding deflection of the deflectable linkage, pivotal motion of the first and second linking segments relative to the intermediate segment about the first and second pivot axes occurs in a fixed ratio defined by the partial gear engagement.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to surgical implants and, in particular,it concerns an adjustable implant including a telescopic body.

It is known to employ adjustable implants which may be inserted into thebody and then expand or otherwise change shape to assume a final shape.The present invention relates primarily, although not exclusively, to asubset of such devices in which the implant includes a telescopic body.i.e., where a body includes first and second portions which undergorelative motion towards and/or away from each other so that a length ofthe telescopic body can be varied.

SUMMARY OF THE INVENTION

The present invention is an adjustable implant.

According to the teachings of the present invention there is provided,an adjustable implant comprising: (a) a telescopic body comprising afirst portion and a second portion, the first and second portions beingin sliding engagement such that a length of the telescopic body isadjustable from a first length to a second length; and (b) a deflectablelinkage comprising a first linking segment, an intermediate segmentpivotally connected to the first linking segment about a first pivotaxis, and a second linking segment pivotally connected to theintermediate segment about a second pivot axis, the first linkingsegment being pivotally connected to the first portion and the secondlinking segment being pivotally connected to the second portion suchthat adjustment of a length of the telescopic body causes acorresponding deflection of the deflectable linkage, wherein the firstlinking segment and the second linking segment are formed withprojecting features configured to provide a partial gear engagementbetween the first and second linking segments such that, duringadjustment of a length of the telescopic body and correspondingdeflection of the deflectable linkage, pivotal motion of the first andsecond linking segments relative to the intermediate segment about thefirst and second pivot axes occurs in a fixed ratio defined by thepartial gear engagement, and wherein the telescopic body and thedeflectable linkage form at least part of an implant for deploymentwithin a human body.

According to a further feature of an embodiment of the presentinvention, the projecting features define a gear tooth engaged in acomplementary gear trough.

According to a further feature of an embodiment of the presentinvention, the partial gear engagement is configured such that pivotalmotion of the first and second linking segments relative to theintermediate segment occurs equally and oppositely.

There is also provided according to the teachings of an embodiment ofthe present invention, an adjustable implant comprising: (a) a bodyhaving a length; (b) a deflectable linkage comprising a first linkingsegment, an intermediate segment pivotally connected to the firstlinking segment about a first pivot axis, and a second linking segmentpivotally connected to the intermediate segment about a second pivotaxis, the first linking segment being pivotally connected to the bodyabout a third pivot axis and the second linking segment being pivotallyconnected to the body about a fourth pivot axis; and (c) a mechanism foradjusting a distance between the third and fourth pivot axes, therebycausing deflection of the deflectable linkage, wherein the first linkingsegment and the second linking segment are formed with projectingfeatures configured to provide a partial gear engagement between thefirst and second linking segments such that, during adjustment of thedistance between the third and fourth pivot axes, pivotal motion of thefirst and second linking segments relative to the intermediate segmentabout the first and second pivot axes occurs in a fixed ratio defined bythe partial gear engagement, and wherein the body and the deflectablelinkage form at least part of an implant for deployment within a humanbody.

According to a further feature of an embodiment of the presentinvention, the mechanism for adjusting a distance between the third andfourth pivot axes comprises a screw actuated mechanism for adjusting alength of the body.

According to a further feature of an embodiment of the presentinvention, the mechanism for adjusting a distance between the third andfourth pivot axes comprises a telescopic adjustment mechanism foradjusting a length of the body.

According to a further feature of an embodiment of the presentinvention, the projecting features define a gear tooth engaged in acomplementary gear trough.

According to a further feature of an embodiment of the presentinvention, the partial gear engagement is configured such that pivotalmotion of the first and second linking segments relative to theintermediate segment occurs equally and oppositely.

There is also provided according to the teachings of an embodiment ofthe present invention, an adjustable implant comprising: (a) atelescopic body comprising a first portion and a second portion, thefirst and second portions being in sliding engagement such that a lengthof the telescopic body is adjustable from a first length to a secondlength; and (b) a deflectable linkage comprising at least twointerconnected segments including a first end segment and a second endsegment, the first end segment being in articulated connection with thefirst portion and the second end segment being in articulated connectionwith the second portion such that adjustment of a length of thetelescopic body causes a corresponding deflection of the deflectablelinkage, wherein the first portion and the second end segment are formedwith complementary cooperating surfaces shaped such that, duringadjustment of a length of the telescopic body and correspondingdeflection of the deflectable linkage, relative motion of the firstportion and the second end segment maintains the cooperating surfaces instrain-limiting proximity, and wherein the telescopic body and thedeflectable linkage form at least part of an implant for deploymentwithin a human body.

According to a further feature of an embodiment of the presentinvention, the cooperating surfaces are configured to avoid contact inan unstressed form of the implant.

According to a further feature of an embodiment of the presentinvention, the cooperating surface of the second end segment includes aconvexly curved bulge.

According to a further feature of an embodiment of the presentinvention, each of the first end segment and the second end segment ispivotally interconnected with an intermediate segment so as to bepivotable relative to the intermediate segment about respective firstand second spaced-apart pivot axes.

According to a further feature of an embodiment of the presentinvention, the intermediate segment is formed with a tissue contactsurface that extends along more than half a maximum length of thetelescopic body.

According to a further feature of an embodiment of the presentinvention, the first end segment and the second end segment areinterconnected so as to be relatively pivotable about a pivot axis.

According to a further feature of an embodiment of the presentinvention, the first end segment is formed with a tissue contact surfacethat extends along more than half a maximum length of the telescopicbody.

There is also provided according to the teachings of an embodiment ofthe present invention, an adjustable implant comprising: (a) atelescopic body comprising a first portion and a second portion, thefirst and second portions being in sliding engagement such that a lengthof the telescopic body along an axis of the telescopic body isadjustable; and (b) a headless bolt deployed in a region of overlapbetween the first and second portions, the headless bolt having athreaded outer surface and having first end and second end abutmentsurfaces, wherein the first portion is formed with entrapment featuresconfigured to abut at least one of the first end and second end abutmentsurfaces of the bolt so as to prevent displacement of the bolt relativeto the first portion in at least one direction along the axis, andwherein the second portion is formed with at least one elongatedthreaded surface deployed to engage the threaded outer surface of thebolt, the elongated threaded surface having a length greater than alength of the headless bolt, and wherein the telescopic body forms atleast part of an implant for deployment within a human body.

According to a further feature of an embodiment of the presentinvention, a length of the headless bolt is less than the range ofadjustment.

According to a further feature of an embodiment of the presentinvention, the length of the elongated threaded surface is sufficient tospan a range of adjustment corresponding to a difference between a firstlength and a second length of the telescopic body.

According to a further feature of an embodiment of the presentinvention, the at least one elongated threaded surface is implemented asat least two elongated threaded surfaces deployed to engage spaced-apartregions of the threaded outer surface of the bolt.

According to a further feature of an embodiment of the presentinvention, the sliding engagement of the first and second portions isdefined by sliding abutment surfaces of the first portion including twoinward-facing walls, and sliding abutment surfaces of the second portionthat are provided together with the clongatcd threaded surfaces bysurfaces of two elongated projections, the elongated projections beingshaped and sized to span a gap between the inward-facing walls and thethreaded outer surface of the bolt.

According to a further feature of an embodiment of the presentinvention, the first portion includes two elongated projections carryingthe entrapment features.

According to a further feature of an embodiment of the presentinvention, there is also provided a deflectable linkage comprising atleast two interconnected segments including a first end segment and asecond end segment, the first end segment being in articulatedconnection with the first portion and the second end segment being inarticulated connection with the second portion such that adjustment of alength of the telescopic body causes a corresponding deflection of thedeflectable linkage.

According to a further feature of an embodiment of the presentinvention, the deflectable linkage further comprises an intermediatesegment, deflection of the deflectable linkage resulting in a change inspacing between the intermediate segment and the telescopic body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIGS. 1A-1C are isometric views of an adjustable implant, constructedand operative according to a first embodiment of the present invention,shown in a collapsed state, a semi-deployed state, and a fully deployedstate, respectively;

FIG. 2 is an exploded isometric view of the adjustable implant of FIGS.1A-1C;

FIG. 3 is a partially assembled isometric view of the adjustable implantof FIGS. 1A-1C;

FIGS. 4A-4C are side, top and bottom views, respectively, of theadjustable implant of FIGS. 1A-1C;

FIG. 4D is a view similar to FIG. 4A showing a variant implementation ofa partial gear engagement between two linking segments of the implant;

FIGS. 5A-5C are cross-sectional views taken along the line A-A in FIG.4C, the adjustable implant being shown in a collapsed state, asemi-deployed state, and a fully deployed state, respectively;

FIGS. 6A-6D are side views of the adjustable implant of FIGS. 1A-IC in acollapsed state, two intermediate positions, and a fully deployed state,respectively, illustrating a strain-limiting configuration according toan aspect of the present invention;

FIG. 7A is an isometric view of an alternative implementation of anadjustable implant, constructed and operative according to an embodimentof the present invention, shown in a semi-deployed state;

FIG. 7B is a center-plane cross-sectional view taken through theadjustable implant of FIG. 7A:

FIG. 8 is an exploded isometric view of the adjustable implant of FIG.7A;

FIGS. 9A and 9B are side views of a further implementation of anadjustable implant, constructed and operative according to an embodimentof the present invention, shown in a collapsed state and a deployedstate, respectively;

FIG. 10 is an exploded isometric view of the adjustable implant of FIGS.9A and 9B; and

FIGS. 11A and 11B are isometric views of a further variantimplementation of an adjustable implant, constructed and operativeaccording to an embodiment of the present invention, shown in acollapsed state and a deployed state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an adjustable implant.

The principles and operation of adjustable implants according to thepresent invention may be better understood with reference to thedrawings and the accompanying description.

By way of introduction before addressing the drawings in detail, thepresent invention encompasses a number of points of novelty which areexemplified by the various embodiments disclosed herein, but which eachhave utility independently in a range of other implementations andapplications. For example, the embodiments of FIGS. 1A-8 illustrate afirst aspect of the present invention which provides a gear-likemechanical engagement between links of a four-pivot-axis adjustableimplant structure to define the adjustment motion. The embodiments ofFIGS. 1A-6D and 9A-10 illustrate a second aspect of the presentinvention according to which complementary cooperating surfaces distinctfrom the articulating joints of an adjustable implant are shaped andpositioned such that they provide additional support under conditions ofloading of the implant to oppose the resulting strain. A third aspect ofthe present invention exemplified in the various illustrated embodimentsrelates to a mechanism for adjusting the length of a telescopic body,and hence adjusting the state of the implant. It should be noted thatthe first and second aspects of the invention may equally be implementedin adjustable implants which employ adjustment mechanisms other than thetelescopic adjustment of the second aspect of the present invention, andthat the telescopic body adjustment mechanism may be used in any or allimplants which change their length, without requiring the features ofthe other aspects of the invention, and in some cases, without thepresence of any deflectable linkage of the types to which the otheraspects of the invention apply.

Referring now to the drawings. FIGS. 1A-6D illustrate a first embodimentof an adjustable implant, generally designated 10, illustrative ofcertain aspects of the present invention.

Adjustable implant 10 has a telescopic body 12 including a first portion14 and a second portion 16. First and second portions 14 and 16 are insliding engagement such that a length of the telescopic body isadjustable from a first length to a second length. In the embodimentshown, adjustable implant 10 also has a deflectable linkage including atleast two, and in this case three, interconnected segments 18, 20 and 22of which segment 18 is a first end segment (or “linking segment”) inarticulated connection with first portion 14 and segment 22 is a secondend segment (or “linking segment”) in articulated connection with secondportion 16. The structure is such that adjustment of a length of thetelescopic body causes a corresponding deflection of the deflectablelinkage, as best illustrated in FIGS. 5A-5C where progressive decreasein the length of telescopic body 12 from L₁ through L₂ to L₃ causesprogressive deflection of the deflectable linkage, in this casecorresponding to parallel motion of the intermediate segment 20 awayfrom telescopic body 12, to increase the height of implant 10 from aninitial low-profile H₁ through H₂ to H₃.

Implant 10 of this example has four distinct pivotal connections eachhaving one or more pivot pin whose central axis defines a distinct pivotaxis: a first pivot axis 24 between first end segment 18 andintermediate segment 20; a second pivot axis 26 between intermediatesegment 20 and second end segment 22; a third pivot axis 28 betweenfirst end segment 18 and first portion 14; and a fourth pivot axis 30between second end segment 22 and second portion 16. (In the explodedview of FIG. 2, the corresponding openings for receiving the pivot pinsare labeled with the corresponding numerals primed.) The distancebetween pivot axes 28 and 30 is adjustable, in this case by telescopicadjustment of telescopic body 12, so as to adjust the shape of theimplant. However, a structure with rigid links interconnected at fourpivot axes does not inherently define a unique geometry, and could inprinciple allow a rocking motion of intermediate segment 20 relative totelescopic body 12. A first aspect of the present invention addressesthis issue by reducing the degrees of freedom of the four-pivot-axis sothat rotation about two adjacent axes, in this case, axes 24 and 26occurs in a fixed ratio, most preferably equal and opposite. Thisresults in a stable and well-defined orientation of intermediate segment20 at every stage of the adjustment process, providing, for example,parallel motion between telescopic body 12 and intermediate segment 20as illustrated here.

Structurally, in the implementation illustrated here, first linkingsegment 18 and second linking segment 22 are formed with projectingfeatures configured to provide a partial gear engagement between thesegments. Specifically, in this case, first linking segment 18 is formedwith a gear tooth 32 while second linking segment 22 is formed withprojections defining therebetween a complementary tooth trough 34 forreceiving gear tooth 32. Tooth 32 and trough 34 are preferably partialprofiles of corresponding virtual gear wheels centered at pivot axes 24and 26, respectively, and most preferably have standard involute geargeometry, as is well known in the field of gears. Given the limitedrange of angular motion of the implant from its collapsed state to itsfully deployed state, in certain cases as illustrated here, it has beenfound sufficient to include a single gear tooth 32 and singlecorresponding inter-tooth trough 34. However, alternativeimplementations employ two or more teeth and associated troughs on oneor both of the linking segments, for example, to provide reliableengagement for an implant with a larger range of angles and/or usingsmaller size teeth. By way of one further non-limiting example, FIG. 4Dshows schematically a variant implementation in which the gearconfiguration is implemented with a plurality of teeth, specifically,two teeth 32 and one interposed trough 34 as part of segment 18 and twotroughs 34 with one interposed tooth 32 as part of segment 22.

Although a conventional gear tooth shape is believed to be advantageous,it should be noted that alternative forms of “gear engagement” betweenthe two linking segments may also be used. Various non-standard toothshapes, or even a transverse pin (i.e., projecting parallel to the pivotaxes) on one linking segment engaged in a slot extending radially fromthe pivot axis of the other linking segment, can provide a sufficientlygood approximation to a fixed ratio of rotation between the two linkingsegments.

In the particular case illustrated here, the inter-axis lengths oflinking segment 18 (between axes 24, 28) and linking segment 22 (betweenaxes 26, 30) are equal, and the partial gear engagement employstooth/trough profiles corresponding to virtual gears of the samesizes/angular pitch. As a result, the line between axes 24 and 26,corresponding to the orientation of intermediate segment 20, remainsparallel to the length of telescopic body 12 (or a line joining axes 28and 30). By employing linking segments of differing inter-axis lengthsand/or by employing an asymmetric partial gear engagement, other desiredgeometries of motion can be achieved, such as various combinations ofadjustable spacing and angle of inclination. In each case, however, theform of the motion is predefined by the structure, and the device ispreferably stable against any rocking motion in each position over itsrange of motion.

This aspect of the present invention may be implemented in any implantin which the distance between axes 28 and 30 can be adjusted. Examplesinclude any and all cases in which a screw (boll) is employed to adjusta length of a base/body between axes 28 and 30, and all forms oftelescopic bodies, whether using an internal adjustment mechanism suchas that described herein or whether adjusted by an external/removableactuator mechanism. Additionally, this aspect of the present inventionmay be implemented in cases where a base of the implant is of fixedlength, but where an adjustment mechanism displaces one or both of pivotaxes 28 and 30 along the base so as to vary a distance between them.

It will be noted that the aforementioned pivot axes do not necessarilycorrespond to the extremities of the corresponding segments.Particularly notable is that intermediate segment 20 is formed with atissue contact surface 21 which, in particularly preferredimplementations, extends along more than half a maximum length of thetelescopic body. This tissue contact surface together with theoutward-facing lower surface(s) of telescopic body 12 provide opposingcontact surfaces which, on adjustment of the implant, can be used topush apart tissues to achieve a desired extent of separation,distraction or height restoration, all according to the particularapplication.

Turning now to a second aspect of the invention, this is applicable incases where relative motion of parts of the body/base cause deflectionof a deflectable linkage, such as the three-segment linkage ofadjustable implant 10 or a two-segment linkage such as that ofadjustable implant 200 described below. The motion of the adjustableimplants described herein is primarily defined by the geometry of thepivot axes and adjustment of the telescopic body, optionally furtherdefined by a partial gear arrangement according to the first aspect ofthe present invention described above. However, under conditions ofsignificant applied loading, it may be preferable that part of the loadis borne by structures other than the pivot connections.

To this end, in the example of adjustable implant 10, first portion 14of telescopic body 12 and second end segment 22 of the deflectablelinkage are formed with complementary cooperating surfaces shaped suchthat, during adjustment of a length of telescopic body 12 andcorresponding deflection of the deflectable linkage, relative motion offirst portion 14 and second end segment 22 maintains the cooperatingsurfaces in strain-limiting proximity. “Strain-limiting proximity” isused herein in the description and claims to refer to two componentswhich are either in contact with each other or which are in proximitywith each other to the extent that, when a load is applied to theimplant sufficient to elastically deform the implant, the surfaces ofthe components come into contact within the range of elasticdeformation. i.e., before the elastic limit of any of the components isexceeded. In certain particularly preferred embodiments, such contactoccurs during the “initial stages” of elastic deformation which, forthis purpose, may be defined as the first 50%, more preferably the first10%, and most preferably the first 5%, of linear strain as a proportionof the maximum strain which would bring the implant to its elasticlimit. In this manner, the complementary cooperating surfaceseffectively serve as a “stop” to limit or resist elastic deformation ofthe implant, thereby improving the performance of the implant as a wholeunder conditions of loading. In certain alternative embodiments, aninitial gap between the components in strain-limiting proximity may bechosen to be in excess of 50% of the maximum strain which would bringthe implant to its elastic limit. This option may be particularlyadvantageous where it is desired to provide relatively high flexibilityof the implant during routine loading while ensuring that thedeformation “bottoms-out” and is stopped before approaching levels whichmight result in damage.

Structurally, this strain-limiting (deformation-limiting) feature ismost preferably implemented as illustrated here by providing a smallabutment surface or edge 36 at the extremity of first portion 14 and aconvexly curved bulge 38 along a lower edge of second end segment 22.The shape of the convexly curved bulge is calculated (or empiricallyderived) to match the path of relative motion between second end segment22 and edge 36 as the implant is adjusted through its range of motion,thereby ensuring that the desired proximity is maintained throughout therange. FIGS. 6A-61) illustrate a sequence of states spanning the rangeof adjustment, and illustrate a clearance 40 which is preferablymaintained according to certain implementations of the present inventionbetween edge 36 and the adjacent region of bulge 38. This clearance asobserved in the unstressed state of the implant is in certain preferredimplementations small compared to the dimensions of the implant,typically amounting to no more than 10%, and more preferably 5%, of theoverall dimension of the implant in the direction of the spacing, evenin the collapsed state. This clearance preferably remains substantiallyconstant over the range of adjustment of the implant, for example, mostpreferably varying by no more than ±20%. Provision of a small clearancein the unloaded state of the implant may be advantageous in that itensures that the strain-limiting features do not add significantfrictional resistance to a process of adjusting the implant shape, atleast until a stage of deployment where significant loading isencountered. It may also provide a relatively high-flexibility state, asmentioned above.

Throughout the exemplary embodiments described herein, each of the“segments” described may be implemented as a unitary body, as abilateral “forked” structure, or as a bilateral pair of separateelements which once assembled move in unison and are functionallyequivalent to a single “segment”. In adjustable implant 10 asillustrated here, first and second end (linking) segments 18 and 22 areforked elements which extend bilaterally on either side of intermediatesegment 20 which is disposed internally to those segments. In thecontext of the strain-limiting features, it will be appreciated thatthese features may be provided on only one side of the forked second endsegment 22 or, more preferably, on both sides thereof, therebymaximizing the structural support provided by these configurations underconditions of loading.

The strain-limiting features according to this aspect of the presentinvention may be implemented in a range of different types of implant,and with a range of different adjustment mechanisms. By way of onefurther non-limiting example, FIGS. 9A-10 illustrate implementation ofthese features in the context of an adjustable-angle implant 200 inwhich a first end segment 218 and a second end segment 222 areinterconnected so as to be relatively pivotable about a pivot axis 224.(Features of implant 200 that are analogous to features of implant 10will be denoted by the same reference numerals with addition of 200 tothe number.) First end segment 218 is preferably formed with a tissuecontact surface 219 that extends along a major dimension having a lengthmore than half a maximum length of a telescopic body formed by a firstportion 214 and a second portion 216. The result is an implant which hasan adjustable angle between tissue contact surface 219 and an outwardlyfacing tissue contact surface 213 of the telescopic base. In thiscontext, the preferred implementation of adjustable-angle implant 200 asshown also includes strain-limiting features, structurally andfunctionally equivalent to those described above, including abutmentsurface or edge 236 and convexly-curved bulge 238. These and otherfeatures of implant 200 will be fully understood by analogy to thedescription of implant 10 above and from the further discussion of thestructure and function of these implants described below.

Turning now to a third aspect of the present invention, the variousembodiments of an adjustable implant illustrated herein also exemplifyan adjustment mechanism for adjusting a length of a telescopic bodywhich forms at least part of an implant. For conciseness ofpresentation, this aspect of the invention is illustrated herein in thecontext of an adjustable implant of implant 10, where a change in lengthof the telescopic body effects a change to a height of a deflectablelinkage. It should be noted however that this aspect of the presentinvention may be used to advantage in any implant with telescopicadjustment, even if no such deflectable linkage is present, and may beused to advantage in applications in which an initially minimum-lengthimplant is to be extended once within the body as well as applicationwhere an initially maximum-length implant is to be shortened within thebody. The mechanism may also be useful in application whereunidirectional actuation (i.e., just elongation or just shortening)without reversibility is sufficient.

Referring now particularly to FIGS. 2 and 3, first and second portions14 and 16 are here configured for sliding engagement such that a lengthof the telescopic body along an axis of the telescopic body isadjustable. A headless bolt 42, having a threaded outer surface 44between two end abutment surfaces 46, is deployed in a region of overlapbetween the first and second portions. First portion 14 is formed withentrapment features configured to abut at least one, and preferablyboth, end abutment surfaces of bolt 42 so as to prevent displacement ofbolt 42 relative to first portion 14 in at least one direction along theaxis of the telescopic body. Second portion 16 is formed with at leastone, and preferably two, elongated threaded surfaces 48 a and 48 b,deployed to engage the threaded outer surface of the bolt. Elongatedthreaded surfaces 48 a and 48 b have a length greater than a length ofheadless bolt 42.

In the non-limiting preferred example of implant 10, the entrapmentfeatures of first portion 14 include the upper and lower edges of a slot50 into which bolt 42 is inserted during assembly, such that the upperand lower edges of the slot abut end abutment surfaces 46 to preventaxial displacement of the bolt relative to first portion 14. Rotation ofbolt in that inserted position engages and draws inwards (or ifreversed, forces outwards) elongated threaded surfaces 48 a and 48 b,thereby adjusting a length of telescopic body 12.

The term “headless bolt” is used herein to refer to a bolt which doesnot have a head of diameter greater than the threaded shaft of the bolt.In order to allow turning of bolt 42 to adjust the length of telescopicbody 12, one of end abutment surfaces 46 is preferably formed with ashaped recess, which may be a shallow recess or a through-bore passingalong the length of the bolt, to receive a correspondingly shaped tooltip.

The use of a “trapped” headless bolt 42 within first portion 14 andrelatively long threaded surfaces 48 a, 48 b, allows the use of a boltwhich in some embodiments is shorter than the range of adjustment of thedevice. This may provide certain advantages such as leaving a largerarea available for openings through the implant, for example, to allowbone ingrowth through the implant. Where the bolt is relatively short,the range of adjustment of the telescopic body is typically definedprimarily by the length of elongated threaded surfaces 48 a, 48 b, whichpreferably span the range of adjustment corresponding to a differencebetween a first length L₁ and a second length L₃ (FIGS. 5A-5C oftelescopic body 12.

A range of implementations of the elongated threaded surface(s) may beused. In the particularly preferred non-limiting example of implant 10,the elongated threaded surfaces are integrated with elongatedprojections 52 which also define sliding abutment surfaces as part ofthe sliding engagement with first portion 14. Specifically, firstportion 16 is here formed with two inward-facing walls 54. Outersurfaces of elongated projections 52 are configured to move in slidingengagement with inward-facing walls 54 to define the sliding engagementbetween first and second portions 14 and 16, while the inward-facingelongated threaded surfaces 48 a, 48 b engage threaded outer surface 44of bolt 42. Elongated projections 52 are preferably shaped and sized tospan a gap between inward-facing walls 54 and threaded outer surface 44of bolt 42, such that contact between elongated projections 52 and walls54 prevents any outward flexing of projections 52 and maintains reliableengagement of elongated threaded surfaces 48 a, 48 b with threaded outersurface 44 of bolt 42.

The operation of the adjustment mechanism can be best understood fromFIGS. 5A-5C. In FIG. 5A, bolt 42 is engaged with the extremities ofthreaded surfaces 48 a (and 48 b), corresponding to the longest state L₁of telescopic body 12 which, in this embodiment, is also the lowestheight H₁ configuration for insertion into the body. A suitable tool(not shown) is then inserted along an access channel from the right sideof telescopic body 12 as shown, and is used to turn bolt 42. As itturns, engagement of bolt 42 with threaded surfaces 48 a (and 48 b)draws second portion 16 towards first portion 14, as seen in thesuccessive positions of FIGS. 5B and 5C. Longitudinal motion of bolt 42relative to first portion 14 is prevented by the abutment of the ends ofbolt 42 against the top and bottom edges of slot 50. In this example, asthe length progressively decreases through L₂ to L₃, the deflectablelinkage is progressively deflected to increasing heights of H₂ and H₃,until the end of the range of motion is reached, typically definedeither by reaching the end of the thread or by reaching mechanicalabutment, for example, of second portion 16 against first portion 14.

Turning now to FIGS. 7A-8, it should be noted that the trapped, headlessbolt approach may be implemented using a wide range of differentstructures both for the entrapment features and for the elongatedthreaded surfaces. By way of one further non-limiting example, FIGS.7A-8 illustrate an alternative implementation of an adjustable implant,generally designated 100, constructed and operative according to afurther embodiment of the present invention. Implant 100 is generallyanalogous to implant 10 described above, and equivalent features arelabeled with similar reference numerals incremented by 100.

In this case, first portion 114 includes two elongated projections 156carrying entrapment features in the form of cut-outs 158 which providesurfaces abutting end abutment surfaces 146 of headless bolt 142. Secondportion 116 in this case is formed as a block with inward-facingelongated threaded surfaces 148 that are subdivided by slots 160 whichare shaped to receive projection 156. By positioning bolt 142 withincut-outs 158 and introducing the ends of elongated projections 156 intothe beginnings of slots 160, threaded outer surface 144 is brought upagainst the start of elongated threaded surfaces 148 such that rotationof bolt 142 by a suitable tool (not shown) causes bolt 142 to drawsecond portion 116 and first portion 114 together. The remainingstructural features and function of implant 100 will be understood byanalogy to that of implant 10 described above.

Turning now to FIGS. 9A-10, these illustrate variable-angle implant 200which was described above in the context of the strain-limitingfeatures. As best seen in the exploded view of FIG. 10, the telescopicadjustment mechanism employed in this example is essentially identicalto that of implant 10 described above, with equivalent elements labeledsimilarly with addition of 200 to the reference numerals.

Turning now to FIGS. 11A and 11B, these illustrate a further embodimentof a variable-angle implant, generally designated 300. The structure andfunction of implant 300 are to a large extent analogous to that ofimplant 10 described above, and similar elements are designated bysimilar reference numerals with addition of 30) to the number.

Implant 300 is a variable-angle implant, functionally analogous toimplant 200, but differs from implant 200 primarily in that the firstportion of the telescopic body is here implemented as two rigidlyinterconnected or integrally formed sections 314 a and 314 b.(Projection 362 provides an anchor point for a delivery system (notshown) for the implant and is not a pivot.) The effect of this firstportion structure is to position the pivotal connection 328 betweenfirst portion 314 b and first end segment 318 in the mid-half (i.e.,between 25% and 75%) of the maximum length of the implant, and incertain preferred implementations, at a relatively high position abovean initial height of pivotal connection 324. This geometry facilitates arange of angles of tissue contact surface 319 which spans from a“negative angle” as shown in FIG. 11A to a “positive angle” as shown inFIG. 11B. The negative angle initial configuration may provideadvantages in certain application during insertion of the implant intothe body by providing a low profile leading end and a wedge-like overallprofile for progressively separating tissues during insertion. Here too,the exemplary non-limiting adjustment mechanism for the telescopic bodyis essentially similar to that of implant 10 described above, and willnot be described further.

All of the above exemplary embodiments are suitable for use, as is orwith minor modifications that will be self-explanatory to a person ofordinary skill in the art, in a wide range of orthopedic applications,and especially in cases where a distance, spacing and/or angle betweentwo tissue surfaces is to be increased or adjusted. One non-limitingfield of particular relevance is spinal surgery, including devices forintra-body, inter-body placement within or between adjacent vertebralbodies. The devices are typically delivered in a low-profile form whileheld by an elongated holder (not shown), are inserted to the desiredtarget location, and are then adjusted to provide the desired degree oftissue separation and/or angular correction. For intervertebral fusionapplications, the devices may be used for any approach directionincluding, but not limited to, various posterior and lateral approachroutes. Various bone-ingrowth openings (for example, as illustrated) arepreferably provided to facilitate fusion and/or osteo-integration.

It should be noted that embodiments of the present invention whichprovide “parallel” adjustment of spacing between tissue contact surfacesdo not necessarily, or even typically, have contact surfaces which areparallel per se. Thus, for example, an upper tissue contact surface 21of implant 10 as best seen in FIGS. 5A-5C is shown with a preset inclineto provide slight lordotic angle restoration in addition to an overallanatomically-rounded shape towards its extremities. Furthermore, thetissue contact surfaces are typically modified by various ridges,projection or other features to enhance mechanical anchoring againsttissue surfaces, as well as openings as mentioned above.

The disclosed implants may be formed from any and all materials orcombinations of materials known to be suitable for implementation ofsurgical implants. Examples include, but are not limited to, titanium,surgical stainless steel and polymers such as PEEK.

Except where stated otherwise, it should be noted that the variousstructures illustrated herein as being implemented on either a proximalor a distal end of an implant should be understood to be reversible.Thus, where features are described as being part of a first portion ofthe telescopic body or a first end segment of a deflectable linkage andare illustrated as being a proximal structure, these structures canreadily be adapted for implementation at a distal end of the implant,and vice versa.

It will be appreciated that the above descriptions are intended only toserve as examples, and that many other embodiments are possible withinthe scope of the present invention as defined in the appended claims.

1. A method of deploying an adjustable implant comprising the steps of:providing an adjustable implant having a deflectable linkage and atelescopic body, wherein the deflectable linkage includes at least twointerconnected segments including a first linking segment and a secondlinking segment, wherein the telescopic body includes a first portionand a second portion, and wherein the first portion and the secondlinking segment are formed with complementary cooperating surfaces;adjusting a length of the telescopic body from a first length to asecond length; deflecting the deflectable linkage; and maintaining thecomplementary cooperating surfaces of the first portion and the secondlinking segment in strain-limiting proximity during adjustment of thelength of the telescopic body and corresponding deflection of thedeflectable linkage.
 2. The method of claim 1 further comprising thestep of sliding the first portion relative to the second portion whenadjusting the length of the telescopic body.
 3. The method of claim 1further comprising the step of avoiding contact of the complementarycooperating surfaces when the implant is an unstressed form.
 4. Themethod of claim 1 wherein each one of the first portion and the secondlinking segment includes two of the one or more complementarycooperating surfaces.
 5. The method of claim 1 wherein the deflectablelinkage includes an intermediate segment, wherein each of the firstlinking segment and the second linking segment is pivotallyinterconnected with the intermediate segment.
 6. The method of claim 1wherein the cooperating surface of the second linking segment includes aconvexly curved bulge.
 7. The method of claim 1 further comprising thestep of decreasing the length of the telescopic body increases adistance between a first contact surface of the telescopic body and asecond contact surface of the deflectable linkage.
 8. A method ofdeploying an adjustable implant comprising the steps of: providing anadjustable implant having a deflectable linkage and a telescopic body,wherein each of the deflectable linkage and the telescopic body areformed with a complementary cooperating surface; deploying the implantfrom a collapsed state to a deployed state different from the collapsedstate; and maintaining the complementary cooperating surfaces of thedeflectable linkage and the telescopic body in strain-limiting proximityduring deployment of the implant from the collapsed state to thedeployed state.
 9. The method of claim 8 wherein the cooperating surfaceof the deflectable linkage includes a convexly curved bulge.
 10. Themethod of claim 8 further comprising the step of adjusting a length ofthe telescopic body.
 11. The method of claim 10 further comprising thestep of decreasing the length of the telescopic body increases adistance between a first contact surface of the telescopic body and asecond contact surface of the deflectable linkage.
 12. The method ofclaim 8 wherein the deflectable linkage includes at least twointerconnected segments including a first linking segment and a secondlinking segment, wherein the telescopic body includes a first portionand a second portion, and wherein the first portion and the secondlinking segment are formed with the complementary cooperating surfaces.13. The method of claim 12 wherein the deflectable linkage includes anintermediate segment, wherein each of the first linking segment and thesecond linking segment is pivotally interconnected with the intermediatesegment.
 14. The method of claim 12 wherein each one of the firstportion and the second linking segment includes two of the one or morecomplementary cooperating surfaces.
 15. A method of deploying anadjustable implant comprising the steps of: providing an adjustableimplant having a deflectable linkage and a telescopic body, wherein thetelescopic body includes a first portion and a second portion, whereinthe deflectable linkage includes a first linking segment, anintermediate segment pivotally connected to the first linking segmentabout a first pivot axis, and a second linking segment pivotallyconnected to the intermediate segment about a second pivot axis, thefirst linking segment being pivotally connected to the first portion andthe second linking segment being pivotally connected to the secondportion, and wherein the first linking segment and the second linkingsegment are formed with projecting features configured to provide apartial gear engagement directly between the first linking segment andthe second linking segment; adjusting a length of the telescopic bodyfrom a first length to a second length; deflecting the deflectablelinkage; and pivoting the first linking segment and the second linkingsegment relative to the intermediate segment about the first and secondpivot axes occurs in a fixed ratio defined by the partial gearengagement.
 16. The method of claim 15 wherein the projecting featuresdefine a gear tooth engaged in a complementary gear trough.
 17. Themethod of claim 15 wherein the pivoting the first linking segment andthe second linking segment relative to the intermediate segment occursequally and oppositely.
 18. The method of claim 15 wherein thetelescopic body includes a first contact surface with a first tissue andthe intermediate segment includes a second contact surface with a secondtissue opposite to the first tissue, wherein decreasing the length ofthe telescoping body increases a distance between the first contactsurface of the telescopic body and the second contact surface of theintermediate segment.
 19. The method of claim 15 comprising the step ofmaintaining complementary cooperating surfaces of the first portion andthe second linking segment in strain-limiting proximity duringadjustment of the length of the telescopic body and correspondingdeflection of the deflectable linkage.
 20. The method of claim 19wherein the complementary cooperating surface of the second linkingsegment includes a convexly curved bulge.